Organic Acids and amino acids are used for a variety of purposes in the pharmaceutical, health and food industries. Especially preferred are the L-isomer forms of organic acids and amino acids.
L-malic acid is an organic acid that is used primarily in pharmaceutical applications as an antidote for hyper-ammoniemia and as a component of amino acid infusion. L-malic acid also presents interest as a food acidulant in competition with citric acid for, for example, confectionary products. Further uses include that of a flavoring agent in a wide range of foods such as nonalcoholic beverages, candy and canned fruits and vegetables.
L-aspartic acid is an amino acid widely utilized in the food industry as a flavoring agent.
Organic acids and amino acids have conventionally been produced by chemical synthesis. However, chemically synthesizing amino acids and organic acids (for example, the chemical synthesis of malic acid from maleic anhydride and water) generally produces the amino acid or the organic acid as an optically inactive mixture (DL-isomer). Such mixtures must then be subjected to a separation process to remove the natural L-isomer from the DL-mixture.
To overcome the problems associated with such DL-isomer mixtures, resort has been made to the use of various microorganisms to synthesize (produce) organic acids and amino acids. Such use of microorganisms provides a biospecificity and selectivity to the enzymatic reaction to permit conversion of a substrate to the natural L-form of the organic acid or amino acid which is generally unavailable in chemical synthesis. This biospecificity and selectivity offers advantages of total product yield, product quality and a significant reduction in waste disposal, production of the natural L-form of the organic acid and/or amino acid produced thereby.
The use of various microorganisms to enzymatically convert fumaric acid to the natural L-form of malic acid has been disclosed. Such strains include those of the species Lactobacillus brevis, Lactobacillus delbrueckii and E. coli (U.S. Pat. No. 2,972,566) and the genus Paracolobacterium aerogenoides (U.S. Pat. No. 3,980,520). Furthermore, the use of a variety of fumarase-producing microorganisms, such as Brevibacterium ammoniagenes, Corynebacterium egui, Xanthobacter flavus, Proteus vulgaris and Pichia farinosa (U.S. Pat. No. 3,922,195), have all been disclosed for the conversion of fumaric acid to malic acid.
The use of various microorganisms to convert fumaric acid (ammonium salt) to L-aspartic acid has also been reported. Strains of E. coli, Brevibacterium metalcoligenes, Serratia and Pseudomonas putida have all been disclosed for this purpose. Further, the use of Brevibacterium ammoniagenes to convert ammonium fumarate to L-aspartic acid has also been described in U.S. Pat. No. 4,138,292.
Unfortunately, while the biospecificity and selectivity of the enzymatic reaction using the disclosed microorganisms offers certain advantages relating to the production of the natural L-form of malic acid, aspartic acid and/or other organic acids and/or amino acids, there nonetheless remains a need to improve the efficacy of these processes and to identify and use previously unconsidered species of microorganisms therefor.
Microorganisms of the genus Microbacterium are well known and described [see Bergey's Manual of Systematic Bacteriology, Volume 2, Section 15 at Pages 1320-1322 (1986)]. Even though strains of Microbacterium are fumarase producers, we are not aware of the use of microorganisms of the genus Microbacterium for the production of L-malic and/or L-aspartic acid.
Accordingly, it can be seen that there remains a need to identify and utilize other microorganisms which are capable of efficiently and effectively producing organic acids and/or amino acids, such as L-Malic acid and/or L-Aspartic acid, on an industrial scale.